The CX4 itself can only address 2 MiB when in lorom mode (plus native support for bankswitching in a 3rd megabyte by switching between the "one 2 MiB ROM" and "two 1 MiB ROMs" control register.

So whatever this ROM hack is doing, those extra 2 MiB have to be doing something different. I'd arbitrarily guess that there's a separate ROM that's there only for the SNES's CPU and the CX4 can't address.

Just curious how. My guess would be tieing both EPROM /CE lines to GND and connect A20 to /CE1 and /CE2 of the Cx4, but I'm not sure. I've succesfully used one 27c160 by doing that on a 2DC0N board but that's it.

Just curious how. My guess would be tieing both EPROM /CE lines to GND and connect A20 to /CE1 and /CE2 of the Cx4, but I'm not sure. I've succesfully used one 27c160 by doing that on a 2DC0N board but that's it.

Just to briefly explain this:

There's a register ($7F52) in the CX4 that controls, when operating in LoROM layout, whether it expects one 2 MiB ROM, or two 1 MiB ROMs.

When the bit is set, ROM1 is enabled for all ROM access and ROMA20 is driven accordingly.When the bit is clear, ROM2 is enabled when ROMA20 would have been high. (I don't know what A20 is doing at this time)

In this way, the software could bankswitch between 3 total MiB of stuff, but not more. And FPZ doesn't do this anyway.

The hack may not be compatible with the original Cx4 hardware. The implementation on the SD2SNES and in emulation might be able to support larger ROM sizes while the original can't. If only the S-CPU needs access to the additional ROM and not the Cx4 then you could make a circuit that would work if you prevent the Cx4 from responding to the address range that the new ROM data is mapped. However if the Cx4 needs to be able to access this data and the original chip can't address it then you're probably out of luck.

This isn't unusual because in the past many translations and ROM hacks were developed on emulators and later found out to not work on the real hardware.

Currently I'm using a 2DC0N pcb with two am29f016b eeprom and a 139 decoder for my testSo I'll need to make cx4 pin high. It seems on the pcb there is a pad especially for that, I'll give it a try.

But just to be sure before...Do I need to make some modification to my rom file prior to those test?Ie: converting it into hirom format using 32kb dummy file?If so, they'll become 2x32mb eeprom.No problem since I have some 29f033c.

I'm more a hardware guy, dont know a lot about rom mapping.I've put the hirom info on my previous post, but sincerely, I dont know alot about it.

Coincidentally, the $7f52 ROM selection is one of the few things still not emulated by my new Cx4 implementation in bsnes-plus (and the bizarre HiROM layout is another one). I guess I should probably consider doing so.

I think the bizarre HiROM layout is only a weird thing you need to emulate if you want to call the pins on the CX4 always the same thing regardless of how the mapping pin is strapped.

The same output pins always relay SNESA0-A14 and SNESA16-A19; the only difference is how those outputs are connected to the ROM's high address lines. The out-of-order-ness shown in qwertymodo's pinout (13 14 20 15 16) insinuates to me that the naïve map was intended to be HiROM and they did the simplest useful thing for LoROM compatibility.

Here is some update. I've been able to have the rom to boot on the cartridge in lorom mode.But when it load it shows interface register, immmediate register and immediate rom error.When I try to lunch the game, the capcom logo and intro music starts.. then nothing... I get black screen, then a purple screen .

Here is how I wired my stuff.First I used a FPZ rom hack that I splitted into 2x16mb2xam29f016b eeprom and retrostage fx adapterthe eeprom /ce lines are connected to a 139 decoder.Decoder enabler is vss and inputs are A21 (cx4 pin15) ans vssLast I connected both eeprom A20 directly to the cx4 RA20 (pin34).

Here is a picture of my working boardSorry about the fuzzy wiring, its kind of a test board, so I needed to have quick access to /oe, /cs, vss and vcc

Is the issue with the romhack or my build?I think we are really close to it, a bit of help would be appreciated

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